The present invention relates to an improved non-contact detection type rotary encoder, and more particularly relates to improvements in the output characteristics of a rotary encoder which includes a circular recording medium having a recorded pattern magnetized along the periphery thereof and mounted to a central rotary shaft and a detection head spaced from and facing the recorded pattern on the recording medium.
A conventional rotary encoder of the above-described type in generally has a construction in which a central rotary shaft is coaxially held in a hollow, cylindrical housing and a detection head is fixedly arranged within the housing while spacedly facing a recorded pattern magnetized along the periphery of a circular recording medium mounted to the rotary shaft. As the recording medium rotates, a magnetic field applied to the detection head changes depending on the recorded pattern on the recording medium and, in response to such change in the magnetic field, the detection head generates a series of output signals representative of the recorded pattern on the recording medium. Generation of the output signals is carried out free of trouble as long as the clearance between the recording medium and the detection head is kept constant.
In practice, however, the clearance often fluctuates due to warps developed on the recording medium, improper mounting of the recording medium and inherent contortion caused by poor precision in production. Such fluctuations in clearance greatly disturb stability in output characteristics, thereby seriously degrading the SN ratio and precision in detection.